Rewiring Reason is a nice feature – you can use all the Reason synths, effects and instruments in Logic Pro (it should work even in Express Edition). Basis is the so called Rewire protocoll which has been invented by Propellerhead before a good while.
Basically its pretty forward to wire both application together. You just need to know that one of the apps should be the Master, while the other is the slave. Usually you have Logic Pro as the Master, from which you control everything and Reason only as some kind of big effect box.
To start with it, please open Logic Pro and afterwards Propellerhead Reason – NOT vice versa. The master needs to be opened first.
Then create a new track in Logic. The type is “External MIDI”.
In Reason, step up to highest hardware component, the hardware device. There is a button called “Adv. Midi Device”. Click it.
In Logic you are now able to choose Reason in the Library. Just select your “External MIDI” Track and open the Library. You’ll see a folder called “Reason” and then several instruments, depending of what you created. I have chosen one called “Synth”.
Now the signal should go into Reason and do things, but you need to wire it back into Logic to hear it. This can be done with a new track in Logic, an AUX track. You can create it in the Mixer view in “Options > Create new Aux”. Once done you are able to choose the channel which comes from Reason in Logics “I/O” section. I have chosen R/Cha 9/10. If you choose the stereo sum: this already works, but if you want to separate between different channels you need to patch the reason components. I wanted to use the single outputs, so, back to reason.
In Reason you can choose in Options that you would like to view the Rack from the back.
Choose the instrument you want and patch two cabels from the for example master out in the hardware controller on top. The hardware controller finally decides which channels you can hear in Logic. Because I have choosen 9 and 10, my stereo out from the instrument goes into the hardware device in slot 9 and 10 too.
Once done, this is finished and you have successfully rewired Logic to Reason and vice versa. Now your creativity can begin and learning start 
Enjoy!
Enjoy!
